3.2 chromosomes Flashcards
how is the genetic material in prokaryotes stored
- free in NUCLEOID (no nucleus)
- prokaryote DNA (‘naked dna’)
- single chromosome, circular DNA (not associated w proteins for additional packaging)
what cells have plasmids?
some prokaryotic cells
(Plasmids are additional circular DNA molecules)
what are plasmids?
small, circular DNA
- may contain one or several genes
- bacteria can easily exchange plasmids
- can self-replicate
steps to become eukaryote chromosomes 5
- dna coiled around 8 histone proteins – nucleosome
- nucleosomes linked by additional histone protein – string of chromatosomes
- coil to form solenoid structure – condensed to form 30 nm fibre
- fibres form loops, compressed and folded around proteins to form chromatin
- chromatin supercoil during cell div into chromosomes
what is the constriction point??? of a chromosome. and what are the shorter and longer sections called
centromere
shorter section – p arm
longer section – q arm
how can the unique banding patterns on chromosomes be generated
staining
what is a locus
a position of a particular gene on a chromosome
three points of reference for the region of a locus
- number/letter that denotes WHICH CHROMOSOME
- which ARM the locus is on (q or p)
- number corresponding to the G BAND location
what are organismms wtih TWO sets of chromosomes called
diploid
diploid divided by 2 =
haploid (sex cells/gametes)
what is a zygote
a diploid cell resultant from the fusion of 2 gametes
characteristics of a diploid nuclei
- nuclei possessing PAIRS of HOMOLOGOUS chromosomes (2n)
- two alleles for each trait
- all body/somatic cells are diploid
characteristics of haploid nuclei
- only 1 set of chromosomes (n)
- possess a SINGLE allele for each trait
- all gametes are haploid (from diploid cells via meiosis)
characteristics of homologous chromosomes
- carry same set of genes in diff locations
- each allele (diff versions of the same gene) comes from each parent
what are alleles
diff versions of the same gene
what are the common stuff between homologous chromosomes
- same structural features
- same genes at the same loci (may have diff allele
what is a karyotype
the number and types of chromosomes
in a eukaryotic cell
method karyotypes are determined
- harvesting cells from foetus or WBC
- chemically inducing cell division, arresting mitosis while chromosomes are condensed
(stage halted will determine if the chromosomes appear w sister chromatids)
how does a karyogram work
(it looks like all the homogolous chromosomes but 1-22 + x and y)
- chromosomes stained and photographed
- chromosomes arranged into homologous pairs according to size
why cant species interbreed
- diff diploid numbers – cannot form homologous pairs in zygotes
- offspring are infertile, cannot form functional gametes
heterosomes vs autosomes
heterosomes: determines sex
autosomes: does not
why karyotype an unborn child
- determine gender
- test for chromosomal abnormalities
down sydrome
- 3 pairs of chromosome 21
- caused by non-disjunction event
- mental and physical delays in development
what is a non-disjunction event?
seperation fails – both sister chromatids/homologous chromosomes are pulled to same pole
genome size comparison: viruses and bacteria, prokaryotes, eukaryotes, plant
viruses and bacteria: very small
prokaryotes: smaller than eukaryotes
plant: varied (plants can self fertilise)
what is the technique for meausring length of DNA molecules and who founded it
autoradiography
john cairns
what does autoradiography do
for measuring the length of DNA molecules
- visualise chromosomes whilst uncoiled
old method to find chromosome length that was inaccurate
measured while condensed during mitosis – inaccurate due to supercoiling
what did cairns technique discover about DNA replication 2
- DNA replication involves formation of a replication bubble (while prokaryotic involves a single origin of replication)
- DNA replication is bi-directional (occurs independently at both ends of replication bubble)
cairns technique steps (6 steps)
- cells grown in solution with RADIOACTIVE THYMIDINE
- tritiated thymidine is INCORPORATED into CHROMOSOMAL DNA
- chromosomes are isolated by LYSING the cells fixing the chromosomes to a photographic surface
- RADIATION released converts Ag+ IONS in SILVER BROMIDE into INSOLUBLE metal grains
- EXCESS silver bromide is washed away, leaving silver grains as SMALL BLACK DOTS
- when the film is developed, chromosomal DNA can be VISUALISED with a ELECTION MICROSCOPE
identifying gene loci and its polypeptide product using databases?? name the 2 (i dont know why youd need this)
genbank / omim
